(1) Field of the Invention
The present invention relates generally to the repair and maintenance of nuclear reactor pressure vessel heads and, more particularly, to a tool positioning device for positioning tools to repair defects adjacent to sealing grooves in a nuclear reactor pressure vessel head.
(2) Description of the Prior Art
The reactor pressure vessels (PVs) of pressurized water nuclear reactors (PWRs) and boiling water reactors (BWRs) must be opened periodically for maintenance and/or repair. This process involves lifting the reactor head for access to the reactor internals and later reinstalling the head when maintenance is complete. For certain types of PWR's this maintenance includes replacing two O-rings on the underside of the reactor head perimeter. Because the reactor heads are quite heavy, in some cases weighing over 20 tons, and quite large, reaching diameters over 20 feet, it is impractical to turns heads over for easy access to the O-rings. As a consequence, workers replacing the O-rings must work over their heads in an awkward fashion. Aligning tools correctly for work on the PV head can be difficult particularly as workers begin to tire. Compounding the problem is the fact that the reactor head may be quite radioactive requiring workers to wear bulky protective clothing.
The reactors which are the object of the present invention may include two concentric O-rings which are recessed into the PV head. As will be discussed in more detail below, steps are taken to ensure that hardware components used to hold the O-rings in place do not fall into the reactor core.
It follows that any tool which can expedite whatever steps are necessary to replace the O-rings will result in cost savings by reducing reactor down time, reduced personnel radiation exposure, and provide a better quality finished product.
Thus, there remains a need for a new and improved tool for working on the underside of a PV head that permits precise placement of a tool while, at the same time, reduces worker fatigue and radiation exposure time.